serikali ya mapinduzi zanzibar care tanzania and department

This vegetation type represents public land, which has been annexed to the Ngezi
Forest Reserve. This area was not botanically assessed, but it is likely to contain a rich
diversity of annual and perennial weeds.
4.1.3 Indicator species and criteria to diagnose ecological condition/integrity
Biological indicator species predict the environmental quality of the community
ecosystem. A forest is sound if it is able to sustain its structure when faced with
regular and incidental natural perturbations. The main criterion for forest integrity is
the occurrence of all species and age classes in a particular proportion of social
organization (Herlocker 1999). The loss of any one species is an indication of poor
forest condition. The change in the relative abundance of various species forms the
basis of community indicators, which can be detected by establishment of long term
monitoring programmes (Spellerberg 1991).
Plants and animal populations exist in community ecosystems under different regimes
of environmental conditions including climate, soil and moisture content. Not only
loss of a particular species that counts for community (forest) integrity, but fluctuating
climatic conditions also affect the ecological conditions which inflict vegetation
change. Indicator species have been used in mineral prospecting or as soil pH
indicators. Heathland community is found on oligotrophic acid soils and the
indicators are low growing, dwarf ericoid shrubs e.g. Erica mafiensis whose
population forms over 90%. It has very low species diversity. This is a unique
habitat, which is very fragile.
Some tree species are declining or disappearing through over-harvesting for timber
and other forest products (medicines, building material, edible fruits). Croton
sylvaticus is over used as medicinal plant. Indigenous timber trees include Milicia
excelsa, Bombax rhodognaphalon, and Afzelia quanzensis. Abandoned logs, cut
stumps and planks on the market, foot-trails to harvested sites are good indicators of
the decline of timber trees. There are also reports that big companies carried tree
harvesting of these species. Between 1957 and 1964 an Indian, V.R. Joshi used Ngezi
Forest to harvest timber; the Zanzibar Government was also involved in timber
harvesting from 1964 to 1966, while the Chinese did the same from 1975-1979.
Although timber harvesting has been suspended there were many indications of illegal
harvesting, these included fresh cut logs and trails to harvesting sites.
The Government replenished the forest by introducing exotic timber trees of
Calophyllum inophyllum, Cordia alliodora, Grevillea robusta, Khaya anthotheca,
Terminalia ivorensis, Maesopsis eminii, Tabebuia triphylla, Tectona grandis and
Cedrella mexicana. Some of these are aggressive invaders on the regeneration of the
indigenous species. The main aggressors are Cedrella mexicana, Maesopsis eminii,
Cordia alliodora and Terminalia ivorensis (H. Selemani pers.comm. 2005).
I. Structural indicators
Natural vegetation is considered stable when it is undisturbed. Where a forest is
disturbed through man-made interactions the likes of fire, land clearance, collection of
fuel wood and medicines, building materials and timber harvesting, the ecological
ecosystem (forest integrity) is also affected (Budowski 1965). Forest structural
indicators, therefore, can define the ecological integrity of the habitat.
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